Safety method, device and system for an energy storage device

ABSTRACT

A method, device and system is disclosed for rapidly and safely discharging remaining energy stored in an electrochemical battery  104  in the event of an internal short circuit or other fault. In its best mode of implementation, if a sensor  116  detects one or more parameters such as battery temperature  204  or pressure  206 , exceeding a predetermined threshold value  334 , the terminals  144  of the battery or cell are intentionally short-circuited external to the battery through a low or near zero resistance load  150  which rapidly drains energy from the battery  104 . Heat generated by such rapid drain is absorbed by a heat absorbing material  151  such as an endothermic phase-change material like paraffin. The rate energy is drained via the external discharge load  150  may be controlled with an electronic circuit  136  responsive to factors such as state of charge and battery temperature. Devices such as inductive charging coils  160 , piezoelectric and Peltier devices  300 , may also be used as emergency energy discharge loads. Heat absorption material  163  may be used to protect adjacent issue in medically-implanted devices.

REFERENCE TO PRIOR-FILED APPLICATIONS

This application is a Continuation-in-part of co-pending PCT ApplicationPCT/US02/35698 filed Nov. 6, 2002, which is a Continuation-in-part ofU.S. patent application Ser. No. 10/014,757 filed Nov. 7, 2001 now U.S.Pat. No. 6,531,847; and a Continuation-in-part of co-pending PCTApplication PCT/US03/00565 filed Jan. 8, 2003, which claims priority toU.S. patent application Ser. No. 10/042,898 filed Jan. 9, 2002 now U.S.Pat. No. 6,586,912, the disclosure of each of which is incorporatedherein by reference.

TECHNICAL FIELD

The invention relates generally to electrochemical storage cells(hereinafter referred to as “batteries”), and more particularly tosafety circuits and systems to rapidly drain energy from a battery inthe event of a fault or other malfunction.

BACKGROUND

Batteries are now in use in a wide range of applications. This range ofapplications is expected to increase in the future as storage batterytechnology, particularly energy density, continues to improve. In recentyears, implanted biomedical batteries have become important for poweringso-called bionic devices such as cochlear implants, neuromuscularstimulators, cardiac pacemakers and defibrillators, and artificialorgans. In addition, batteries have become an essential power source ina wide range of portable electronic devices including computers,personal information managers, radio telephones (“cellular telephones”),global positioning satellite (GPS) devices, and other devices thatcombine the functions of the foregoing. The safety of these devices isparamount as the explosion of a battery in any of these devices couldcause injury and death.

Batteries may present certain safety problems under a variety ofcircumstances. These potential problems can become more acute, even lifethreatening, when they are implanted in a human being. These problemsmay include internal short-circuits, over-pressure leading to bulgingenclosures, electrolyte leaks, explosion, over-heating and combustion.Such faults can result from both internal and external factors. Theycannot be tolerated in any implanted battery, and could lead to serioussafety problems in any application.

The present invention is fundamentally an emergency energy drain or“dump” system. That is, in the event of a serious fault such as aninternal short circuit, the remaining energy in the battery is quicklydischarged by diverting it to a discharge radiator or sink acting tosafely dissipate or absorb the heat generated by the current sodiverted. While it is commonly accepted in the art that rapidly draininga battery would cause it to dangerously increase its heating, tests haveshown that this counter-intuitive approach is highly effective inpreventing dangerous over-heating and/or rupture of batteries thatexperience an internal short circuit.

The present invention is particularly suited for human-implantablebatteries, however may be applied to any electrochemical storage device,or even inertial energy storage devices such as flywheels.

Battery safety circuits and devices in general are widely used in bothprimary (disposable) and secondary (rechargeable) batteries and chargingcircuits. The circuits typically limit charging and discharging, ordisconnect a battery in the event of over-heating or over-pressure inthe battery. These devices are intended to prevent real-world failures,but are also designed to meet certain industry and regulatory testrequirements such as nail penetration and mechanical crush tests.

U.S. Pat. No. 6,210,824 issued to Sullivan, et al., for example,discloses an end-cap incorporating a pressure sensitive switch intendedto disconnect the battery from a circuit in the event pressure insidethe battery casing becomes excessive.

Similarly, U.S. Pat. No. 5,766,793 issued to Kameishi et al. discloses abi-metal plate that bends when heated due to overcharging or shortcircuiting, breaking the external circuit.

U.S. Pat. No. 6,242,893 issued to Freedman discloses a battery chargingcircuit which interrupts the charging or discharging of a battery toprevent over-charging or over-discharging.

U.S. Pat. No. 6,268,713 issued to Thandiwe discloses a method wherein abattery charger controller (circuit) detecting a fault isolates one ormore batteries while simultaneously notifying a user or host device.

U.S. Pat. No. 5,898,356 issued to Gascoyne et al. discloses athermally-activated switch which by-passes a cell with an open circuit.

U.S. Pat. No. 6,172,482 issued to Eguchi discloses a battery protectioncircuit comprising a thermally-activated fuse intended to preventover-charging.

U.S. Pat. No. 5,684,663 issued to Mitter discloses a resettable circuitintended to protect a battery pack from an external short bydisconnecting the battery pack from the faulty load by means of acontrol FET until the fault is cleared.

Similarly, U.S. Pat. No. 5,625,273 issued to Fehling et al. discloses alatching circuit intended to disconnect an external device from thebattery in the event of sensing a fault (over-heating, voltage reversalor short circuit).

Each of the foregoing approaches fails to mitigate over-heating causedby a short circuit internal to a battery (as opposed to battery heatingcaused by an external short). Such faults are generally addressed in theindustry by a so-called “safety separator” made of a porous materialthat, when heated to a specific temperature, fuses (becomes impermeable)and electrically isolates a cathode from an anode, shutting down theelectrochemical reaction. For example, U.S. Pat. No. 6,127,438 issued toHasegawa, et al. discloses a safety separator made of polyethylenemicroporous film with high tensile strength, a 20-80%, porosity, a gelfraction of 1% or more and an average pore diameter determined by thepermeation method of 0.001-0.1 μm, and a method for producing same. Theseparator so disclosed fuses (becomes impermeable) at between 100° C.(212° F.) and 160° C. (320° F.). Additionally, the separator disclosedis claimed to have a breaking time of 20 seconds in silicone oil at 160°C. (320° F.). There are numerous other variations of safety separatorsused in the industry. A short circuit resulting from faulty manufacture,however, such as a contaminant lodged in the components of a batteryduring assembly creating a hole in the separator, growth of dendriteswithin the battery or crushing or penetration of the battery can defeatthe safety features of the safety separator, causing a runaway conditionand overheating.

The large flow of current through such an internal short can cause heatand pressure to rise dramatically inside the battery. Each of theforegoing prior art approaches (both the use of safety circuits andsafety separators) further suffers from the problem that the energystored in the battery may continue to over-heat the battery, causing abuild-up in pressure, explosion or combustion resulting in rupture ofthe battery enclosure, and/or leaks of electrolyte. Thus, a means ofpreventing a runaway condition in the event of the failure or breach ofa safety separator would be highly beneficial.

U.S. Pat. No. 5,478,667 issued to Shackle, et al. discloses a heatdissipation scheme in which the current collectors of a battery serve asa heat sink to help dissipate to the atmosphere heat generated insidethe battery. However, such an arrangement is impractical for smallbatteries, especially those that are medically implanted. Moreover, sucha thermal sink would likely not dissipate heat quickly enough in theevent of an internal short circuit, especially one caused by a suddenpenetration or crushing event. Thus, a passive heat sink such asdescribed in the '667 patent would likely not prevent a runawaycondition and may not be adequate to prevent electrolyte leaks,explosions or even combustion.

A better approach not found in the prior art is to provide an emergencyenergy drain method or device intended to intentionally rapidly depletestored energy to minimize further battery heating and resulting damage.

SUMMARY

The best mode of the present invention comprises a control circuit andsensors which detect faults such as over-heating and over-pressure. Ifsuch conditions persist, even if the external load is disconnected,electrolyte leakage, explosion, and combustion can occur. Therefore,once the control circuit detects conditions above predeterminedthresholds, it connects the faulty cell or cells to an energy “dump” ordischarge device (hereinafter referred to as “discharge device”) such asa heat sink or heat dissipation device such as a low resistance coil. Inmedically implanted devices, it is advantageous to provide a heatabsorption material (“HAM”) around the discharge device to minimizeheating of adjacent tissue. Such HAM preferably takes the form ofparaffin or other material with an endothermic melting phase change atabout between 42° C. and 80° C. Since the preferred embodiment of theclaimed device is automatic, it is advantageous to provide anotification that it has been activated. This is particularly true whenlife-dependent devices (such as implanted cardiac defibrillators) willnecessarily need to be replaced or serviced without delay. The presentinvention can also be implemented as a manually activated system.

In addition, the present invention is equally applicable to relatedenergy storage devices such as super capacitors and so-called“asymmetric hybrid devices” (see e.g., U.S. Pat. No. 6,252,762 issued toAmatucci).

Accordingly, it is an object of the present invention to provide asafety device and method to prevent the dangerous build-up of heat andpressure in batteries that experience internal short circuits.

A more particular object of the present invention is to provide a meansfor draining rapidly and safely remaining stored energy in a battery inthe event of an internal fault.

It is further an object of the present invention to provide a means ofnotifying a user or operator that a battery fault has occurred.

In one aspect of the present invention, an emergency energy dischargesystem is provided comprising: at least one energy storage device; atleast one detecting device for monitoring one or more operatingparameters of said energy storage device; means for storingpredetermined safety threshold values for operating parameters of saidenergy storage device; comparison means for comparing said predeterminedsafety threshold values with said operating parameters; decision meansfor determining whether said operating parameters exceed one or moresaid predetermined operating threshold values; activation meansresponsive to decision means; energy discharge device for dischargingsaid energy stored in said energy storage device so as to render saidenergy storage device safe before the fault or faults causing saidmonitored operating parameters to exceed said safety threshold valuesrenders the energy storage device unsafe; and heat absorbing materialthermally coupled to said energy discharge device. The heat absorbingmaterial may have a melting point about between 42° C. and 80° C., andmay comprise an endothermic phase-change material, which may compriseparaffin. The heat absorbing material may comprise at least one materialselected from the group consisting of: paraffin, polypropylene,polyethylene, SiO2, and water. The heat absorbing material and energydischarge device may be mutually encapsulated in a sealed enclosure. Theemergency energy discharge device may comprise a Peltier device.

In another aspect of the present invention, a battery safety circuit isprovided comprising: one or more first electrochemical cells; at leastone sensor monitoring at least one of the following conditions of saidone or more first electrochemical cells: voltage, change in voltage,rate of change in voltage, current, change in current, rate of change incurrent, state of charge, change in state of charge, rate of change instate of charge, temperature, change in temperature, rate of change intemperature, impedance, change in impedance, rate of change inimpedance, pressure, change in pressure, rate of change in pressure,electrolyte pH, electrolyte specific gravity, amount of bulging ofbattery enclosure, change in amount of bulging of battery enclosure, andrate of change of amount of bulging of battery enclosure; memorystorage; predetermined safety thresholds for said at least onecondition; a comparator circuit; a control circuit; a diverter switchdevice; an energy discharge load; heat absorbing material closelythermally coupled to said energy discharge load; said comparator circuitcomparing said monitored conditions with said stored predeterminedsafety thresholds and signaling said control circuit whenever said atleast one monitored condition exceeds one or more said predeterminedthresholds; said control circuit sending an emergency energy dischargesignal to said diverter switch device in response to signal from saidcomparator circuit; and said diverter switch device causing electrodesof said one or more cells having conditions exceeding said predeterminedthresholds to be connected to said energy discharge load. The heatabsorbing material may comprise an endothermic phase change material,which may comprise paraffin. The heat absorbing material may comprise atleast one material selected from the group consisting of: paraffin,polypropylene, polyethylene, SiO2, and water. The heat absorbingmaterial and energy discharge load may be mutually encapsulated in asealed enclosure.

In another aspect of the present invention, a battery is providedcomprising: one or more electrochemical cells; a charging circuit; acharging control circuit; an electronic device receiving its power fromsaid one or more electrochemical cells; an emergency energy dischargecircuit further comprising at least one sensor monitoring at least oneof the following conditions of said electrochemical cells: voltage,change in voltage, rate of change in voltage, current, change incurrent, rate of change in current, state of charge, change in state ofcharge, rate of change in state of charge, temperature, change intemperature, rate of change in temperature, impedance, change inimpedance, rate of change in impedance, pressure, change in pressure,rate of change in pressure, electrolyte pH, electrolyte specificgravity, amount of bulging of battery enclosure, change in amount ofbulging of battery enclosure, and rate of change of amount of bulging ofbattery enclosure; memory storage; predetermined safety thresholds forsaid at least one condition stored in said memory storage; a comparatorcircuit; a control circuit; a diverter switch; an electrical dischargeload; said comparator circuit comparing said monitored conditions withsaid stored predetermined safety thresholds and signaling said controlcircuit whenever said at least one monitored condition exceeds one ormore said predetermined thresholds; said emergency discharge circuitsending an emergency energy discharge signal to said diverter switch inresponse to signal from said comparator circuit; said diverter switchcausing electrodes of said one or more cells having conditions exceedingsaid predetermined thresholds to be connected to said energy dischargeload. The battery may be implantable, and the electronic device may alsobe implantable. The battery may further comprise heat absorbingmaterial, which may be thermally coupled to said electrical dischargeload, may have a melting point about between 42° C. and 80° C., and maycomprise an endothermic phase-change material, which may compriseparaffin. The heat absorbing material may comprise at least onesubstance selected from the group consisting of: paraffin,polypropylene, polyethylene, SiO2, and water. The heat absorbingmaterial and electrical discharge load may be mutually encapsulated in asealed enclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating the best mode of the presentinvention.

FIG. 2 is a schematic diagram of a battery incorporating an energydischarge circuit utilizing the secondary inductive charging coil in animplantable device as an energy discharge (dump) device.

FIG. 3 is an illustration of the present invention implemented in alarge battery array such as a submarine power source.

FIG. 4 illustrates the use of a Peltier device (sometimes referred to asa thermoelectric cooler) as an energy drain device.

FIG. 5 is a logic flow and schematic diagram showing implementation ofthe best mode of the present invention.

FIG. 6 is a schematic diagram of the present invention using a simplebimetal temperature-sensing switch and a mechanical pressure-sensingswitch as the triggering devices to initiate an emergency energydischarge.

FIG. 7 is a schematic diagram of the present invention implemented as amanually-operated system on a submarine.

FIG. 8 is a schematic diagram illustrating the method used for testingthe present invention in actual batteries.

FIG. 9 is a time vs. temperature graph showing the results of controlledtesting of the present invention during a nail penetration test.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS

Referring to the drawings, FIG. 1 is a schematic diagram illustratingthe best mode of the claimed safety circuit 100 having a battery 104powering an external device 108 (such as a spinal cord stimulator).Sensors 116 and 120 detect temperature and pressure respectively, andare connected to a detector circuit 124, which also measures voltage 128across and current 132 traveling through the battery 104. Predeterminedthreshold values 134 are stored in the memory of the detector circuit124 and, in the event of an internal fault in the battery (e.g.,over-heating of excessive pressure in, or high current flow through thebattery), the detector circuit 124 signals the safety control circuit136 to initiate an emergency energy discharge sequence includingconnection of the terminals 144 a and 144 b of the battery 104 to anenergy discharge device 150. Heat generated by the discharge is absorbedby a heat absorbing material 151, preferably an endothermic phase-changematerial such as paraffin, which is thermally coupled to the energydischarge device 150 and encapsulated by a biocompatable sealedenclosure 152. Simultaneously, the safety control circuit 136 initiatesan alert signal device 154 to alert the operator or user that a failurehas taken place. The safety control circuit 136 may control the rate ofdischarge of energy from the battery 104 by pulsing (alternatinglyconnecting and disconnecting) the battery 104 from the discharge device150.

The use of endothermic phase-change heat absorbing materials 151 toabsorb heat generated by an emergency energy discharge is intended toprevent over-heating of adjacent tissue. The amount of heat energy Qthat can be absorbed by the heat absorbing material 151 is of coursedependent on the quantity and characteristics of the heat absorbingmaterial used. This relationship can be expressed as:Q = ∫_(T_(I))^(T_(f))C_(P) ⋅ 𝕕T + Δ  H_(f)where

-   -   Q represents heat energy absorbed (J/g),    -   T₁ represents initial temperature (° C.),    -   T_(F) represents final temperature (° C.),    -   C_(P) represents the heat capacity of the heat absorbing        material mass (J/g-K), and    -   H_(f) represents the latent heat of fusion (J/g).

Table 1 depicts properties of a preferred heat absorbing material,paraffin, as compared to other materials typically used in batteries intwo different temperature ranges. Also shown are properties ofalternative, but less effective materials polypropylene andpolyethylene. Still other alternative heat absorbing materials can beused; e.g., Aerogel (Si O₂) or water. Note that in the range of roomtemperature (25° C.) to 100° C. and in the range of body temperature(37° C.) to 100° C., a large portion of the heat absorbed by theparaffin occurs during melting of the paraffin, in which 147 J/g areabsorbed due to latent heat of fusion compared with 392 J/g or 352 J/gtotal, respectively. By contrast, polypropylene and polyethylene neverreach their melting point in this range; therefore, all heat absorptionoccurs due to heat capacity. Water has a relatively high heat capacityand can therefore absorb a large amount of heat prior to undergoing aphase change at its boiling point. A large portion of the latent heat ofevaporation can be absorbed into the water at its boiling temperaturewithout the water actually converting to steam.

TABLE 1 Latent Q Q Heat Heat of Melting Latent Heat Boiling (25° C.-(37° C.- Capacity Fusion Temp of Evap Temp 100° C.) 100° C.) (J/g-° C.)(J/g) (° C.) (J/g) (° C.) (J/g) (J/g) Copper 0.385 1083  29  24 Aluminum0.9 658  68  57 Paraffin 3.26 147 58  392  352 Polypropylene 1.83 88 160 137  115 Polyethylene 1.78 276 142  134  112 Water 4.2 337 0 2259 100 315^(l)  265^(l) 2574^(v) 2524^(v) ^(l)Q (J/g) to reach 100° C.,remaining in liquid state ^(v)Q (J/g) to reach vapor state

FIG. 2 illustrates one implementation of the present invention in whichthe secondary inductive charging coil 160 (which normally functions tocharge the battery 104 through a charging circuit 162) is used as theenergy discharge device. In this example, when a faulty batterycondition is detected by a thermocouple 116 or pressure switch 120,(indicating the existence of an internal short circuit orover-pressure), the safety control circuit 136 connects the inductivecharging coil 160, across the terminals 144 a and 144 b of the failedbattery causing it to dissipate energy from the battery 104 in the formof heat, thus preventing the battery 104 itself from heating todangerous levels. The coil 160 is preferably surrounded by HAM 163 toprotect adjacent tissue from damage resulting from heating of the coil160 during an emergency discharge. Components other than or in additionto inductive charging coils may interchangeably be used as an emergencyenergy discharge device. For example, alerting devices such as soundgenerators (e.g., piezoelectric devices, horns, bells, etc.), vibrators,or lights may be used as part of the emergency discharge circuit, aswell as other signaling devices known in the art. All discharge devicesmay be thermally coupled to heat absorbing endothermic phase-changematerial such as paraffin 163 enclosed in a biocompatable safety capsule161.

FIG. 3 illustrates the method of the present invention in a batteryarray 200 such as that used to power submarines and electric vehicles,and in power grid load leveling installations. Here, a detector circuit124 monitors battery conditions including temperature 204, pressure 206,voltage 208, current 210, electrolyte specific gravity 212, andelectrolyte level 214. These values are communicated to the safetycontrol circuit 136, which is programmed to initiate an emergencydischarge sequence in the event of a fault condition in a battery(internal short circuit or over-pressure). Specifically, ifpredetermined parameters, or combinations thereof, stored in the memoryof the safety control circuit 136, are exceeded, the faulty battery 104is isolated from the battery array 200 by bypassing the faulty battery104 in the array circuit. Simultaneously or immediately thereafter, thesafety control circuit 136 signals a relay 220 to connect the terminals144 a and 144 b of the faulty battery 104 across an energy dischargeload 150 such as a resistance heater. The safety control circuit 136 maybe programmed to vary the drain rate by pulsing (connecting anddisconnecting) the discharge or by adjusting the resistance of the load(variable resistor). The detector circuit 124 and safety control circuit136 may be combined or integrated. Typically, they will comprise digitalcircuits, but may take the form of relatively simple electro-mechanicaldevices such as bimetal thermal switches or deformable pressureswitches, both well known in the art. In such a case, over-temperatureor excessive pressure would cause immediate direct connection of theterminals 144 a and 144 b across the energy discharge device 150.

FIG. 4 illustrates the use of a Peltier device 300 used as an energydischarge device. In the event of an internal short circuit in thebattery 104, as detected by a thermocouple 116 or pressure transducer120, the safety control circuit 136 connects the battery terminals 144across the terminals of the Peltier device 300 causing one side 310 toheat-up and the other side 312 to cool down. By placing the cooled side312 in thermal contact with the battery 104 and the heated side inthermal contact with a heat sink 316, the draining of excess heat fromthe battery may be accelerated using the remaining stored electricalenergy in the battery, which drives the Peltier device 300 “heat pump.”The hot side of the Peltier device may be placed in thermal contact withheat absorbing phase-change material such as paraffin 318.

FIG. 5 is a combined logic flow/schematic diagram illustrating theimplementation of the present invention wherein a combination of batteryparameters are monitored and applied to an algorithm to decide whetherto initiate an emergency energy discharge sequence and, if so, controlthe rate. The greater the remaining charge in the battery, the moreurgent is the need to drain remaining energy quickly. Therefore, thefollowing algorithm may advantageously be used to control the rate ofemergency energy discharge:

-   -   If V₁>V₂ and Internal Short Detected, then Initiate Fast        Discharge Mode;    -   If V₁≦V₂ and Internal Short Detected, then Initiate Slow        Discharge Mode, $\begin{matrix}        {{{Where}\quad V_{1}} = {{battery}\quad{voltage}\quad{at}\quad{time}\quad{of}\quad{fault}}} \\        {V_{2} = {{predetermined}\quad{threshold}\quad{{voltage}.}}}        \end{matrix}$

V2 would be set in terms of remaining energy. Normally V2 would be avoltage resulting from a remaining state of charge of approximately 70%,but can range from 50% to 95%. Additionally, multiple thresholds may beset to initiate a range of emergency energy discharge rates. Dependingon the application, additional variations of this algorithm will benecessary. In some cases, the inverse may be required. For example, abattery with a greater charge but a moderate internal short(moderately-rising temperature or pressure) may initiate a sloweremergency energy discharge rate than a battery with a lower remainingcharge but a severe internal short (rapidly rising temperature orpressure).

In the example illustrated in FIG. 5, the safety control circuit 136monitors voltage 208 of the battery 104, current 210 passing through thebattery 104, internal battery impedance 320, battery temperature 204,internal battery pressure 206, and state of charge 212. Other well-knowndirect and indirect measures of the operating state of the battery maysimilarly be used such as measuring the amount of bulging of the batteryenclosure. It then computes rates of change of each of the factors 326and compares 330 them to a look-up table of acceptable or thresholdvalues 334 stored in memory. The safety control circuit 136 theninitiates an emergency energy discharge sequence if one or a combinationof parameters in the values stored in the look-up table 334 are exceededby the measured values. If an emergency energy discharge sequence isinitiated, the safety control circuit 136 causes relay 335 to close thecircuit connecting the battery 104 directly to the discharge device 150.The safety control circuit 136 can vary the rate of drain from thebattery to maintain safe temperatures of the battery and the energydrain device. For example, the rate of drain of the battery may be afunction of the remaining energy in the battery and the rate of increasein temperature 204 and/or pressure 206 of the battery. The rate of drainmay be a function of one or of a combination of the following factors:voltage 208, change in voltage, rate of change in voltage, state ofcharge 212, temperature 204, change in temperature, rate of change intemperature, impedance 320, change in impedance, rate of change inimpedance, pressure 206, change in pressure, rate of change in pressure,electrolyte pH 213, and/or electrolyte specific gravity 214. Such rateof emergency energy discharge may be linear, non-linear, continuous, orintermittent. State of charge is typically determined as a function of abattery's open circuit voltage, usually integrated over a period oftime. However, state of charge may also be measured by such means asspecific gravity of electrolyte and other methods well-known in the art.

FIG. 6 illustrates the simplest form of implementing the presentinvention as an automated device. Here, when a simple electromechanicaldevice such as a bimetal switch reaches a threshold temperature, itconnects the terminals 144 a and 144 b of the battery 104 to a dischargedevice 150. Similarly, a pressure-activated switch 414 could initiatethe drain of energy from the battery by simply being activated bypressure built-up in the battery, pushing contacts 418 a and 418 bclosed causing connection of the terminals 144 a and 144 b of thebattery 104 to the energy discharge load 150, which is surrounded by aheat absorbing endothermic phase-change material 151 such as paraffinand encapsulated in a sealed enclosure 152.

As illustrated by FIG. 7, although this invention is best implemented asan automated system, it can also be manually operated where appropriate.In this example, if an internal fault such as overheating is detected bya sensor 116 and a detector circuit 124 in a faulty battery 440 in alarge battery array 444 such as powering a submarine drive motor 448,the operator may, upon receiving a signal from an alarm 452 or a display453, manually isolate the faulty battery 440 using an isolation switch456, then connect it to an emergency energy discharge load 150.Additionally, discharge loads can take the form of any device thatconverts energy stored in a battery to another form of energy. Forexample, the stored energy could be converted into heat (e.g.,resistance heater), electromagnetic (e.g., light bulb), kinetic (e.g.,flywheel), chemical (e.g., charge another battery), or potential energy(e.g., wind a spring). Obvious to one skilled in the art should be thatthis implementation of the present invention would be applicable in awide range of installations, including, but not limited to, power gridload-leveling installations, photovoltaic storage banks, and the like.

FIG. 8 is a schematic diagram of the set-up that was used to test thepresent invention. In tests, a fully charged 320-mAh lithium ion cell500 with liquid electrolyte was connected to a Yokogawa MobileCorderMV100 recording voltmeter 504. A type K thermocouple 508 was attached tothe battery case 510 and connected to the recording voltmeter, which wascalibrated to record temperature measured by the thermocouple. Thebattery was placed in a jig 512 designed to minimize conductive heatloss, limiting heat dissipation to convective loss. A remotely operatedpneumatic ram 516 quickly drove a nail 517 through the battery.

In addition, the terminals 520 a and 520 b of the battery 500 wereconnected to wires 524 leading to a resistor 530. A second thermocouple534 was bonded to the resistor. The test protocol was to activate theram 516, penetrating the battery 500 with a nail 517, then, one secondlater, close the circuit across the battery terminals 520 a and 520 bthrough the resistor 530.

FIG. 9 discloses the results of testing of the present invention. Trace600 reflects the battery temperature for a pure nail penetration (noexternal energy discharge circuit). Its temperature peaked atapproximately 118° C. (244° F.) in approximately 3 minutes, thengradually dropped to ambient temperature over approximately 25 minutes.

Trace 604 illustrates a similar test showing a “pure external short.”That is, the terminals 520 were connected with a near zero ohmresistance wire, and no nail penetration was initiated. In this case,the battery temperature rose to 105° C. (221° F.) in approximately 4minutes, and remained at or above 100° C. (212° F.) for almost 10minutes. This cell did not reach ambient temperature for over 35minutes.

Trace 608 reflects the result of a nail penetration test with a 10 ohmresistor connected across the terminals of the battery one second afterthe cell was penetrated by a nail. In this case, the battery casetemperature rose to 115° C. (239° F.) in 4 minutes, then graduallydropped to ambient temperature in over 35 minutes.

Trace 612 reflects the results of a nail penetration test with a 1 ohmresistor connected across the terminals of the battery one second afterthe cell was penetrated by a nail. In this case, the battery casetemperature rose to 112° C. (234° F.) in 4.5 minutes, then graduallydropped to ambient temperature in approximately 30 minutes.

Trace 616 reflects the results of a nail penetration test with a 0.47ohm resistor connected across the terminals of the battery one secondafter the cell was penetrated by a nail. In this case, the battery casetemperature rose to 99° C. (212° F.) in 3 minutes, then graduallydropped to ambient temperature in approximately 30 minutes.

Trace 620 reflects the results of a nail penetration test with a 0.008ohm wire connected across the terminals of the battery one second afterthe cell was penetrated by a nail. In this case, the battery casetemperature rose to 85° C. (185° F.) in 4 minutes, stayed relativelylevel below 90° C. (194° F.) for approximately 10 minutes, then rapidlydropped to ambient temperature in approximately 30 minutes.

There is a significant difference between the cell in trace 620 and thatwith no emergency energy drain in case 600, namely a peak temperature of118° C. (244° F.) versus 90° C. (194° F.).

From these test data, it will be clear to those experienced in the artthat, after an internal short is detected, quickly draining remainingenergy from the battery by deliberately connecting the externalterminals across an electrically resistive circuit presents asignificant benefit versus merely allowing the battery to reach its peaktemperature as current flows between anode and cathode inside thebattery through a small internal pathway. These data indicate that, inthe event of an internal short, a low (or near zero) resistance externalshort implemented quickly can prevent overheating leading tocatastrophic failure of the battery enclosure. Initiating the emergencyenergy discharge more quickly after nail penetration would furtherreduce the peak battery temperature.

The specific implementations disclosed above are by way of example andfor enabling persons skilled in the art to implement the invention only.We have made every effort to describe all the embodiments we haveforeseen. There may be embodiments that are unforeseeable and which areinsubstantially different. We have further made every effort to describethe invention, including the best mode of practicing it. Any omission ofany variation of the invention disclosed is not intended to dedicatesuch variation to the public, and all unforeseen and insubstantialvariations are intended to be covered by the claims appended hereto.Accordingly, the invention is not to be limited except by the appendedclaims and legal equivalents.

1. An emergency energy discharge system comprising: at least one energystorage device; at least one detecting device for monitoring one or moreoperating parameters of said energy storage device; means for storingpredetermined safety threshold values for operating parameters of saidenergy storage device; comparison means for comparing said predeterminedsafety threshold values with said operating parameters; decision meansfor determining whether said operating parameters exceed one or moresaid predetermined operating threshold values; activation meansresponsive to decision means; energy discharge device for dischargingsaid energy stored in said energy storage device so as to render saidenergy storage device safe before the fault or faults causing saidmonitored operating parameters to exceed said safety threshold valuesrenders the energy storage device unsafe; and heat absorbing materialthermally coupled to said energy discharge device.
 2. The emergencyenergy discharge system recited in claim 1 wherein said heat absorbingmaterial comprises an endothermic phase-change material.
 3. Theemergency energy discharge system claimed in claim 2 wherein said heatabsorbing material has a melting point about between 42° C. and 80° C.4. The emergency energy discharge system recited in claim 2 wherein saidendothermic phase-change material comprises paraffin.
 5. The emergencyenergy discharge system recited in claim 1 wherein said heat absorbingmaterial comprises at least one material selected from the groupconsisting of: paraffin, polypropylene, polyethylene, SiO₂, and water.6. The emergency energy discharge system recited in claim 1 wherein saidheat absorbing material and said energy discharge device are mutuallyencapsulated in a sealed enclosure.
 7. The emergency energy dischargesystem recited in claim 2 wherein said heat absorbing material and saidenergy discharge device are mutually encapsulated in a sealed enclosure.8. The emergency energy discharge system recited in claim 1 wherein saidenergy discharge device comprises a Peltier device.
 9. The emergencyenergy discharge system recited in claim 6 wherein said energy dischargedevice comprises a Peltier device.
 10. The emergency energy dischargesystem recited in claim 7 wherein said energy discharge device comprisesa Peltier device.
 11. A battery safety circuit comprising: one or morefirst electrochemical cells; at least one sensor monitoring at least oneof the following conditions of said one or more first electrochemicalcells: voltage, change in voltage, rate of change in voltage, current,change in current, rate of change in current, state of charge, change instate of charge, rate of change in state of charge, temperature, changein temperature, rate of change in temperature, impedance, change inimpedance, rate of change in impedance, pressure, change in pressure,rate of change in pressure, electrolyte pH, electrolyte specificgravity, amount of bulging of battery enclosure, change in amount ofbulging of battery enclosure, and rate of change of amount of bulging ofbattery enclosure; memory storage; predetermined safety thresholds forsaid at least one condition; a comparator circuit; a control circuit; adiverter switch device; an energy discharge load; heat absorbingmaterial closely thermally coupled to said energy discharge load; saidcomparator circuit comparing said monitored conditions with said storedpredetermined safety thresholds and signaling said control circuitwhenever said at least one monitored condition exceeds one or more saidpredetermined thresholds; said control circuit sending an emergencyenergy discharge signal to said diverter switch device in response tosignal from said comparator circuit; and said diverter switch devicecausing electrodes of said one or more cells having conditions exceedingsaid predetermined thresholds to be connected to said energy dischargeload.
 12. The battery safety circuit recited in claim 11 wherein saidheat absorbing material comprises an endothermic phase change material.13. The battery safety circuit recited in claim 12 wherein saidendothermic phase change material comprises paraffin.
 14. The batterysafety circuit recited in claim 11 wherein said heat absorbing materialcomprises at least one material selected from the group consisting of:paraffin, polypropylene, polyethylene, SiO₂, and water.
 15. The batterysafety circuit recited in claim 11 wherein said heat absorbing materialand said energy discharge load are mutually encapsulated in a sealedenclosure.
 16. The battery safety circuit recited in claim 12 whereinsaid heat absorbing material and said energy discharge load are mutuallyencapsulated in a sealed enclosure.
 17. An implantable batterycomprising: one or more electrochemical cells; a charging circuit; acharging control circuit; an implanted electronic device receiving itspower from said one or more electrochemical cells; an emergency energydischarge circuit further comprising at least one sensor monitoring atleast one of the following conditions of said electrochemical cells:voltage, change in voltage, rate of change in voltage, current, changein current, rate of change in current, state of charge, change in stateof charge, rate of change in state of charge, temperature, change intemperature, rate of change in temperature, impedance, change inimpedance, rate of change in impedance, pressure, change in pressure,rate of change in pressure, electrolyte pH, electrolyte specificgravity, amount of bulging of battery enclosure, change in amount ofbulging of battery enclosure, and rate of change of amount of bulging ofbattery enclosure; memory storage; predetermined safety thresholds forsaid at least one condition stored in said memory storage; a comparatorcircuit; a control circuit; a diverter switch; an electrical dischargeload; heat absorbing material; said comparator circuit comparing saidmonitored conditions with said stored predetermined safety thresholdsand signaling said control circuit whenever said at least one monitoredcondition exceeds one or more said predetermined thresholds; saidemergency discharge circuit sending an emergency energy discharge signalto said diverter switch in response to signal from said comparatorcircuit; said diverter switch causing electrodes of said one or morecells having conditions exceeding said predetermined thresholds to beconnected to said energy discharge load.
 18. An implantable battery asclaimed in claim 17 wherein said heat absorbing material is thermallycoupled to said electrical discharge load.
 19. An implantable battery asclaimed in claim 17 wherein said heat absorbing material comprises anendothermic phase-change material.
 20. The implantable battery asclaimed in claim 19 wherein said heat absorbing material has a meltingpoint about between 42° C. and 80° C.
 21. An implantable battery asclaimed in claim 19 wherein said endothermic phase-change materialcomprises paraffin.
 22. An implantable battery as claimed in claim 17wherein said heat absorbing material comprises at least one substanceselected from the group consisting of: paraffin, polypropylene,polyethylene, SiO₂, and water.
 23. An implantable battery as claimed inclaim 17 wherein said heat absorbing material and said electricaldischarge load are mutually encapsulated in a sealed enclosure.
 24. Animplantable battery as claimed in claim 19 wherein said heat absorbingmaterial and said electrical discharge load are mutually encapsulated ina sealed enclosure.
 25. A battery comprising: one or moreelectrochemical cells; a charging circuit; a charging control circuit;an electronic device receiving its power from said one or moreelectrochemical cells; an emergency energy discharge circuit furthercomprising at least one sensor monitoring at least one of the followingconditions of said electrochemical cells: voltage, change in voltage,rate of change in voltage, current, change in current, rate of change incurrent, state of charge, change in state of charge, rate of change instate of charge, temperature, change in temperature, rate of change intemperature, impedance, change in impedance, rate of change inimpedance, pressure, change in pressure, rate of change in pressure,electrolyte pH, electrolyte specific gravity, amount of bulging ofbattery enclosure, change in amount of bulging of battery enclosure, andrate of change of amount of bulging of battery enclosure; memorystorage; predetermined safety thresholds for said at least one conditionstored in said memory storage; a comparator circuit; a control circuit;a diverter switch; an electrical discharge load; heat absorbingmaterial; said comparator circuit comparing said monitored conditionswith said stored predetermined safety thresholds and signaling saidcontrol circuit whenever said at least one monitored condition exceedsone or more said predetermined thresholds; said emergency dischargecircuit sending an emergency energy discharge signal to said diverterswitch in response to signal from said comparator circuit; said diverterswitch causing electrodes of said one or more cells having conditionsexceeding said predetermined thresholds to be connected to said energydischarge load.
 26. A battery as claimed in claim 25 wherein said heatabsorbing material is thermally coupled to said electrical dischargeload.
 27. A battery as claimed in claim 25 wherein said heat absorbingmaterial comprises an endothermic phase-change material.
 28. A batteryas claimed in claim 27 wherein said heat absorbing material has amelting point about between 42° C. and 80° C.
 29. A battery as claimedin claim 27 wherein said endothermic phase-change material comprisesparaffin.
 30. A battery as claimed in claim 25 wherein said heatabsorbing material comprises at least one substance selected from thegroup consisting of: paraffin, polypropylene, polyethylene, SiO₂, andwater.
 31. A battery as claimed in claim 25 wherein said heat absorbingmaterial and said electrical discharge load are mutually encapsulated ina sealed enclosure.
 32. A battery as claimed in claim 27 wherein saidheat absorbing material and said electrical discharge load are mutuallyencapsulated in a sealed enclosure.
 33. A battery comprising: one ormore electrochemical cells; a charging circuit; a charging controlcircuit; an electronic device receiving its power from said one or moreelectrochemical cells; an emergency energy discharge circuit furthercomprising at least one sensor monitoring at least one of the followingconditions of said electrochemical cells: voltage, change in voltage,rate of change in voltage, current, change in current, rate of change incurrent, state of charge, change in state of charge, rate of change instate of charge, temperature, change in temperature, rate of change intemperature, impedance, change in impedance, rate of change inimpedance, pressure, change in pressure, rate of change in pressure,electrolyte pH, electrolyte specific gravity, amount of bulging ofbattery enclosure, change in amount of bulging of battery enclosure, andrate of change of amount of bulging of battery enclosure; memorystorage; predetermined safety thresholds for said at least one conditionstored in said memory storage; a comparator circuit; a control circuit;a diverter switch; an electrical discharge load; said comparator circuitcomparing said monitored conditions with said stored predeterminedsafety thresholds and signaling said control circuit whenever said atleast one monitored condition exceeds one or more said predeterminedthresholds; said emergency discharge circuit sending an emergency energydischarge signal to said diverter switch in response to signal from saidcomparator circuit; said diverter switch causing electrodes of said oneor more cells having conditions exceeding said predetermined thresholdsto be connected to said energy discharge load.
 34. A battery as claimedin claim 33 wherein said discharge load comprises one or more componentsof said device.
 35. A battery as claimed in claim 34 wherein said one ormore components of said device is at least one inductive charging coil.36. A battery as claimed in claim 33 further including an alertingsignaling device responsive to said emergency energy discharge circuitto issue an alert when said battery experiences a fault.
 37. A batteryas claimed in claim 36 wherein said electrical discharge load comprisesat least said alerting signaling device.
 38. A battery as claimed inclaim 37 wherein said alerting signaling device comprises one or more ofthe following devices: a radio transmitter, a lamp, a light emittingdiode, a sound generator, a vibrating device.